Condition responsive indicating instrument



NW 9 E. T. JOHNSbN 2,333,793

CONDITION RESPONSIVE INDICATING INSTRUMENT Filed Feb. 29, 1940 2 Sheets-Sheet l 3nventor mil T: c bhnson (Ittorneg NW. 9, 1943. E. TJOHNSON assawa CONDITION RESPONSIVE INDIC ATLNG INSTRUMENT Euvcntor attorney Patented Nov. 9, 1943 connrrrou RESPONSIVE INDICATING' INSTRUMENT Johnson; West Orange, N. J., assignor to v I 1 Thomas A. Edison, Incorporated, West Orange.

N. J., a corporation of New Jersey Application February 29, 1940, Serial No. 321,484

" isclaims. (cl. vs- 570) This invention relates to-instruments .for indicating variationsin a predetermined condition such as temperature, pressure orthe like, and has particular significance to indicating instruments of the type which measure the difierential between two such conditions and to compensated forms of instruments employing the difierential principle. The invention is especially concerned with an improved mechanism for operatively interconnecting the motor means and indicating pointer of an in-.

strument.

It is an object of my invention to provide a compact form of indicating instrument having a highly accurate performance. a

- It is another object of my invention to provide an improved indicating instrument having .a linear (i. e. uniform) scale and a high degree of sensitivity and ruggedness.

It is another object to provideindicating' instruments compensated for errors and/or indicating instruments of the .diiferential type, which have the desirable features just mentioned.

It is another object toprovide an: improved form of compensated instrument wherein the compensation is. uniform throughout the rangeof the instrument. V

It is another object'to provide a mechanism for coupling the motor means of the instrument to the indicating pointer, which is simple in form, linear in its response (1. e., transmission)- characteristic and highly stable in action.

Another object is to provide a coupling mechanism adapted for use in? differential-type indicating instruments andhaving the desirable features just noted.

It will be seen that the coupling mechanism of the instant invention is'particularly well adapted to motor means (for indicating instrument's) of the type having actuated portions that move angularly in response to variations in the condition to be measured-a well-known type of such motor means being the Bourdon spring. The particular suitability of this coupling me'chanismto Bourdon-spring types of instruments arises from the fact that the coupling mechanism provides a linear transmission from the motor means to the indicating pointer of the instrument, and yetpermits a highly compact arrangement of the instrument in that thecoupling mechanism may be positioned and the indicator pointer pivoted each within the circumferentialboundary of the Bourdon spring. In instruments of the difierential type wherein there are employed two Bourdon springs, these springs may becoaxiallyarranged .adjacent' to one another with" the coupling mech anism positioned within the boundary of the springs; yet this mechanism will provide a linear coupling between the springs and the pointer as above mentioned. Although this coupling mechanism is particularly well suited and is illustrated and described inconnection with instru 'ments employing Bourdon springs, it will be understood that no unnecessary limitation of my invention to motor means of the Bourdon-spring type is intended.

In the following description and the appended claims other andallied objects and features of my invention are more fully set forth.

In the description of my invention reference is hadto the accompanying drawings, of which:

Figure 1 is a face view, partly broken away, of

. an indicating instrument incorporating my invention and of a type for indicating temperature at a distance, this kind of instrument being commonly known as a. distance-type thermometer;

. Figure 2 is a view of the mechanism of Figure 1 which couples the motor elements of the instrument to the indicating pointer;

' Figure 3 is a partial cross-sectional view taken substantially along the line 33 of Figure 1; and

Figure 4 is a fragmentary view of an instrument in accordance with my invention as adapted to indicate the differential between two predetermined conditions such as the difference between two distinct pressures.

Reference being had to Figures 1 and 3 there will be seen an indicating instrument in the form of a distance typefthermometer comprising a, circular casing l, preferably molded of Bakelite, onto the open end of which is threaded a bezel 2 for holding a crystal or glass 3. Beneath the glass 3 there is provided a dia1 4 supported by the casing on lugs such as 5.. Pivoted at the center of the dial is an indicating pointer 6 which is moved relative to a suitable scale on the dial to indicate variations in the conditions'being measured.

The actuating or motor means for the instrument may be of a liquid expansion type employing a Bourdon spring 1 as the motor element,

- which spring may have a plurality of turns bent 10111331 end portion of the Bourdonspring being clamped to this bracket by means of a clamping bar In and screws suchas H. The outer end I ofthe Bourdon spring I is fitted onto one end of a short tube l2 and sealed thereto as by soldering. The other end of the tube l2 makes connection with a connector fitting 13 comprising upper and lower parts l3 and I3" suitably threaded together to form an airtight seal therebetween. From this connector fitting there leads a capil1ary...tube.Mtmade forcexample-tof steel. This capillary tube passes out; ofpthe casing through an apertured boss l5 and communicates springs may be coaxially disposed next to each other in a highly compact arrangement, as shown in Figure 3. This second Bourdon spring is sealed at its inner end l1 and is supported at its outer end portion as by the bracket 8 in the manner in which the spring I is supported. Coupled to.the outer end portion of the spring "I"! is a;.capillary tube185(se'e Figure .1) which extends along the tube [2, the connector fitting l3 at its other end with a thermostat or bulb m loland the capillary tube [4 throughout thelength the tube being sealed airtight to the bulb. The bulb is to be positioned at the point 'atwhich'=' the temperature is to be measured and consequently the minimum length of the capillary tube Ill-is determined by the distancesbetweenr-snch.zpoint and the instrument; in practice, this'adistance' may vary anywhere from .a few.. feetto several hundred feet.

The motor system above described+i.je.,s1the system comprising the bulb l6, capillary tube l4, fitting 13'; tube l2-and*-Bourdon1*spr'rng T is "hermetically' sealed to-the-outside 'and completely filled -with-a suitable-thermally" expansive fiuid or eliquid; fv'v'hich rmayftypicallrbe substantially pure mercury. "'Sincethe volume of mercury varies inaccordancewith-its-temperature, "variationsin the: temperature at'themulb 'will cause similarwariationsg-in the volumeof "the *mercury in "the-bulb: 'these volume variations causefmercury to be forced alongthe capillarytulo'e Minto and out of "the-Bourdomspring "l' to "actuate-Jthe "inner end portionf 11"," "of the spring in clockwise and counterclockwisedirections. Ini'theimotorisystem'"just-described: .it"is"parti-cularly "'desirable thatj the ratio oftthe' volumetric cap l'city'-"of "the: bulb" 1'6 'to"that.i1of.'the remaining-'portioniof theisystembe largein order that'the 'Bour'don spring willibemighly"sensitive toivariations in the'temperature"ofthe' bulb' and be fairly insensitive 'to" variations in the temperature" of the other portions" of the'motor system. There are, "howeveggpra'ctical 'restrictions"which set a limit. on the'maximum 'value'jotthisratio. In practice; .thegminimumydiameter, OTJITJhE'bOI'E of. the capillarytubel' lfis not permitted tlofbe smaller than. about" 5010' '.."*When the capillary tube is r r 1a'd;e long,.say,'25, feetor more,,its volumetric. tenacity-becomes appreciable in, relation to that of conveniently sized' 'thermostatid.bulbs; as l a result, Ivariationslin, temperature along .the capillarytube .iyill causeaan actuation of the indic'atinglmeans which lissappreiciablelinfrelation to .the indicating. pointer; of 1. the instrument .in .a

manner .to..cause, the indicating means "to. be i moved. in. accordance with .the. difierential 'in the .aetuations. of ,the .two. motorelements.

This second. motor element ;comprises .a..-Bourdon spring f Flo-which is preferablymadein :all

of the latter, the tube l8 extending out of the i tube [8 is hermetically sealed. The portions of Isl-the,capillarytubes l l and I8 between the instrumentandlthe'bulb [6 are held together in parallel relationto each other by a protective armor i zfl preferablyinthe form of a flexible braided sheath. -..The Bourdon spring I! and capillary tube I8 are also completely filled with the thermally: expansive zflnidmmployed .in: the :moton sysizte'mnabovj'e ed'escrtibed;rwhichi fluid; in: .the:", present ezinstanee; :is: mercurym-Because iofcthessimilarity enfethe'Bonrdonzspr'ing' 1; and 'tzlian'd fofi thevs'imiriarit'yrzand-rproximityfnfiithe cicapiliary :tubeszcou- 'ipledrtn thesasprings -temperaturezyariationslat rtheiinstrunientran'dzalongvithe'ccapillaryiitubesiwill cause: simiiamactuations of :the: Bourdonxsprings, :2:thesenactuaftionso'rappearing as :iangularnmovemoms: iofi'othe::innemeridipontions' of the springs and being in a clockwise direction for altempera- .z;turemise and iini'amounters' clockwise :direction'ior rxaitemperatmreifall.

It is a characteristi'c'ioftheimotor=means above v described thatszit'has. :a' linear response; the Bour- .-40 --pera;tnre'..l*llvdthisuchlaimotorisystem it is lii'ghly uimportantithalt :themechanism couplingthe motor means'ntorstheazindicating :pointerJof the inzxstmment zhavez-a'lsoi aolinear, a'riesponse' fchara'ctertisticiitituez; a :constant movement 'transmitting e'ra'tio rthroughoutothe range: .of ztheoinstrument) snice such a coupling mechanismrwil lzthenipermit rzthemserof va linearly calibrated'idial rthe use of v :suchnaanzlziai'iwill eliminateicriticalness 0f Ladjust- .zmentmfetheiiinstrument .andiitendi'inzthe' end to -make (thesinstmment: more rugged and: tower in cost. It iszmlso: impbrtantirthaththeuooupling mechamismtpooducesazhigh :clegree of: amplifica- -tioniin EmDYBmEIIt'IElHdT be yet stableiiniaction so easztonendenithe sinstrumen't'rhighly sensitive :and

yet free from flutter or vibration ofrithe indii-tcating spointemnand; in .:addition, ;that the coupl'mgzm'echanismspemnt a compact arrangement liofizthemarts:ofzthezinstrument: to permit a reductionv in :ithe zroveralliss'ize iof "the instrument.

fzmhezceoplingrmechanismmow tube-described per- "1 therattainmentnfithesezobj ectives in *a'highwly'smxple manner.

vz'fiheecouplingnmechanismqabove referred'to is designatedniby :the :rreference character 2 lsand ..65 comprises four rigid'l'mks-jomted together to form a+substantialzl@arallelogramm aticlink structure, the:flinksnoflthisw-sttucture ibeingwrepresentedin tic-1e [order on their; appearance; -proceeding;-, in a .cloekwisel directiomabout i the'structure iromvthe respects similarto othe-Bourdonspring has for .70;*lowemlinlcytheyegf a z2,;33 zgrfandafixrespem the ,-advantages,hereinafter-pointed out. ,In view of .the particular-.tyzpevo-f'r difierential mechanism which :I employ for; operatively connecting :t-hese .springs.to.theindicating,pointer fi-ewhich mechanism ishereinafter'.describedwthe'twd Bourdon.-

..ltively. .-.",-,I!he-.-two a adii aoentlinks or: drive: memsbersqzlmndrn 'a-re.-respectively onnectedgtmthe :sBOHEdQQiSDI'iIIES: and -.hand:positicnedvsozthat the aaxise-ofnthesuomt v:common rtocthe'; tworlinks coi-ncidesnwith thatiofvthezBourdomsprings;:siThe connection of the link'23 to the B'ourdonjspring l is made by way of a hub- 26 which extends axially through the spring (see Figure3); the link 23 is staked as-at 21 to the bottom of the hub and the hub is secured to and supported by the spring 1, the connection between the hub and spring being made byfitting' the inner end portion 1" of the spring into a slot28'of the hub and securing the portion 1" in the slot as by soldering. The connection between the link 22 and Bourdon spring I! is made in a manner similar to that between the link 23 and spring "I, the link 22 being staked as at 29 to a hub 30 extending axially through the spring I! and the hub being provided with a slot 3| into'whioh is fitted and secured the inner end portion ll of the spring IT. The outer endsof the links-22 and 23 are operatively connected together-by the links 24 and 25. Since the links and 25 are positioned between the springs 1 and H, the outer end portion 22' of the link 22 (which link is in the particular embodiment positioned below. the spring I1) is offset upwardly to a level just above the top of the spring l'l. Secured to the portion 22' of the link 22 is a short bar 32 which is pivoted at its inner end, as at 32', to the link 25. In order that the effectivelength of the link-22 may be adjusted the bar 32 is adjustably con-- nected to the link 22 as by means of a screw and slot connection 33. 1

Extending axially through the hub 26' is an opening 34 and fitted into the upper and lower end portions of this opening are collars. 35 which serve as bearings for a shaft 33. This shaft rests at its lower end on the upper face 3!! .of the hub 30 and has its upper end'portion 36 projecting through an opening 4 at the center of the dial 4; on this upper end portion of the shaft is mounted the indicating pointer 6;

Secured to the lower end portion of the shaft 36, as by a press fit, is a pinion or follower 31 which meshes with a gear segment 38 integrally formed with the link 24. The gear segment has its axis coinciding with that of the 'pivot pin 39 which joins the links 23 and 24, andis spaced somewhat below the link 23, as for clearance purposes, by means of a spacer 39' embracing the pivot pin 39. v The gear segment 38 is provided with a central opening 38' and on the link 23 there is provided a pin 23' which extends through this opening to act as a stop to prevent the-gear segment from beingmoved out of engagement with the pinion. To-prevent play between the teeth of the pinion and of the gear segment the shaft 36 is biased torsionally by means of a hair i spring 41] secured at its outer end, to a pin 4! on the hub 26 and at its inner end to a small collar M'ontheshaft. I

Since the links 22 and 23 f the structure 2| are respectively directly connected to .the Bourdon springs I1 and 1, these linkswill be moved angularly in accordance: with the actuations of their respective springs, andconsequently, the variations in the angle between these links will represent the algebraic difference in the actuations of the springs. It is a characteristic of a jointed parallelogrammatic structure that a variation in the angle between two adjacent sides of the structure will be accompanied by variations of the same magnitude in the angle between each adjacent links of the structure 2|, or whatis the l same thing, by the extent of the angular movement of the gear segment 38 (about the pivot 39) relative to the link 23. When one of the Bourdon springs is actuatedto an extent equivalent to an error in-the actuation of the other spring, this error will then not be represented by the angular movement of the gear segment about the pivot 39 since the gear segment is turned only in accordance with the difierential between the actuations of the Bourdon springs.

The angular movement imparted to the pinion 31, and thus to the indicating pointer 6, by the gear segment 33 comprises two components: A component of movement caused by the turning of the gear segment 38 about the pivot 39; and a component arising from the planetary movement of thegear segment about the axis of the Bourdon springs, which latter component arises from the turning of the link23 by the Bourdon spring 1 about the shaft 36. The first component in the movement of the indicating pointer is directly proportional to the angular movement of the gear segment 38 about the pivot 39, but is stepped up in the ratio of the magnitude of the radius of the gear segment to that of the pinion 31, this ratio being typically from 10 to 15; thesecond component is directly equal to the angular movement of the link 23 about the shaft 36. Thus, the movement-transmitting ratio between the link 23, to which the Bourdon spring 1 is connected, and. the indicating pointer has a magnitude equal to that of the step-up ratio just mentioned plus unity, the additional quantity being due to the second component in the movement of the pointer, as abovementioned; whereas the movement-transmitting ratio between the link 22 to which the compensating spring H is connected and the indicating pointer is the same as the step-up ratio between the gear segment 38 and the pinion 31. Because of this inequality in the movement-transmittingratios of the couplings between the indicating pointer and the Bourdon springs, the pointer is not moved in a manner'directly proportional to the differential in the actuations of the springs. This inequality in the movement-transmitting ratios may, however, be readily compensated, one means of compensation being nowdescribed.

It is seen thatthe difference in the movementtransmittin-g ratios of the couplings between the indicating'pointer and the Bourdon springs is one that is fixed in value throughout the range of the instrument, since one of these movementtransmitting ratios is the same as that between the gear segment and the pinion and the other ratio'is larger than the first by one. This inequality may therefore be compensated by causing the magnitudes of the actuations of the Bourdon springs, produced in response to a change in the condition the effect of which is to be annulled, to be inversely proportional to the magnitudes of the transmitting ratios of the respective couplings between the springs and the indicating pointer. Say, for example, the movement-transmitting ratio between the gear segment 38 and pinion 37 is 15:1. ment as above described, the movement-transmittingratio between the compensating spring I? and pointer 6 will then be 15:1, whereas that between the motor spring I and the pointer will be 16:1. To compensate accurately for a change in temperature between the instrument and the bulb l6, such temperature'change should produce actuations in the compensating and motor springs the magnitudes of which are respectively In the instruintth ratiozoi 16 snchepredetermined ratio in ;theiresponse of" the springs l'liand' i! .mSYbQ effected by merely sensin the cross sectional areas of the. bores'olf .thecapillary :tubes 2H! and M o h in ltheap oportioniof the'ratio des red in the responseoflth spri s- 'In :the instrument as .above described the sirdioating ipointer rmeved atorregisteruthe din ferentiai between two eprede ermined rendi ions each of which are variable, 20118 I ofiwthese icondi, i ns hem-s -varyin temperat e inthe re i along he-eap arytube -4 and in thero ion a the bulb I6. and the other-'oond tionbeing'merely the varying mpe tu e alens'th cap lla tube, Whfle-thelGQulQl n mechan sm l is par cularly pp ab e to instruments of the type adapt d to measure the diff entia between wo such ar a l s, it will be nderstood tha this one hanism may e also advanteuzeously'e ployed instruments of thetype responsive to variations in but a single condition. in utilizing'the eoue pling-mechanism 1-21 in: an; ipstrumentwof the lat-. er t p one f the-links 22 and 3 w u d b held fixed in :positiom-ithe same as occurs in-rep t f e l nk -22 the in t umen -above dee scribed when the temper ture remains constant at the instrument and along-the capillaryitube MWhereas=thetother link is eoupled to %m0tor element such as. the spring 7.

It will .be seen :that thewcoupling mechanism hereinabov-e described is not ubjeott0=ermrs 0 non-linearity in :its transmission characteristic; this is because the-entiretrammission from the motor means to the indicating means of then-n7 strument is on atlinear, angular basis wherein each operative apart accurately transmits its 'IOWll angular movement to the next. rEor instanee, since the-links or-drive-inemb'ers :22 and- :3 are pivoted-to move about-the axis of :theiBQurdon springs as a center-and aredirectlyzconneclled:tp the Bourdon springs respectively, th y Will be turned about thein ivot axesexactlyrinaccordance with the angular movements oi theinner end'portions 1 and 11-ofthespringsiand'by reason of the linear movement-transmitting characteristics of the parallelogrammatie link structure '2 l the angular movements-.of'the drive members will be transmitted linearly, but in .oppoe site directions, through-the gear segment 38 and pinion 3'! to the indicating pointer.

It is often desirablethat a stop beprovidcdto limit the travel of theindicatinggpcinter -rela-.

tive to the scale on the dial. Suchya stop 'may well bein-the form of a. vpin onvthe dialagainst which thepointer may-abut, one such pin for limiting the pointer-6 .to the-minimumspoint on the scale appearingtia-scfleinlFigure 1. Innr'der that delicate parts of the instrumentsuchas the pointer should not be subjected to undue strain should the bulb I6 :be subjected to temperatures below the minimumtemperatureonthe.scale, I provide a yieldable'connection between the' pointer and the motor means of theinstrument. This yieldable connection'is preferably-provided at a joint in the link structure 2|, 'for example, between the links 2-4 and 25, and may comprise'a pivot pin 43 'on the link which is extended through a slot 44 in thelink 2'4 and biased against the lower end of this slot by a spring 45, the spring-being coiled about'a pin-lion the-link z l, hooked atone render; the edge 0f the link and hearing at the'other end againstthe pin dfl. '-'During the operation of the instrument through its normal range the pin-qfi'is-held-in thelower-end. of the slot 4 l'by the spring; *howeven-should-the series .1 :besetueted-tqmove po nter the min mumipomt on times al -the toppi the peinterby? mon er 4.? vill aus th s rin 45 o ield a d reri ithe m n '43 to emote are throushtheslot 4 A cha ssteristicof thevt p efc up ng meq en-ism -2 l herei -empl yed tha it has a inear respon e as when ver the 'linksrareconn cted t termsubstantia l arali los am- Allure-armesp nse cha acteris i is h hly es r le, w t on ome ceses it mav be desira le to have a couplin me h nism with a l ping "r sp ns cha a teristic. as 2 r rthe pu pose-of .cmnnens tine for nonlinear response c,barristeristies of other partszot the-instrument. n-ai lchfiases=Iima2yichflngerthe effeetivealen thint one-'01" morerof-the: links cf-xthe mechanismr-for :example, by 115116 screw 2 and slot connection 33 tto =change lthe effective :length of the link :22 :as (above described. It will ralsolbe understood %that izmay, :by meansof the screw andzslotfeonneotion :33, very thermovement-ttransmitting ratios between the motor andzindicating meanstofittpartimflarneeds.

In :Figure #4 there 'is shown another -form df indicating instrument in @accordance zwithfmy invention; This linstrumentgappearing as 41, may for :example, the employedutos-measure cthe diflere entialvbetweenitwot predeterminediconliitions such as two .difierent ipressures rand .may%therefore :be termed a differentia1 pressure gauge. "'Ihisigauge comprises two pressurersensitive elements nor Bouridon smings 48'and'4'9 eoaxially' arrangedtone above the 'other 'andeach having, for example. only a fraction of-a-single turn. The springs'are supportedat' one endgas at $0 and there: respectively connected to tubes 5! and 5'2 whic'h may lead 't-o any desired points tobring'the Bourdon springs in communi'cation with "the media the pressures of which'are' to be m'easuredfthe other ends of the springs are-sealed and pivoted as :at 5-3 tolinksfl: and fl respectively; which links con nest the 'Bourdon :springs to a coupling mechanism 56 'ilisposed withinfthe circumferential boundary of the Bouriion springs; this mechanismPis basically of the same' typeas 'that of the coupling mechanism 2 l' heretofore described.

Theeouplirrg mechanism 56, like the=mehapjsrn 2 I is} in the -fo'rm "of afour-side'd link' structure jointed su'bs'tantiallyin parallelogram form, Thismechanism comprises a level" or drive member 51 pivoted at one end near the axis of "the Bourdon springs as at"58=and pivot-ally connected at the other codes at some the link; a right angularlever'or drive member 60 pivoted at'its vertex also at 58 "and having one arm *lying substantially below the arm '51 and pivotaliy con necteda tits 'far endj'as at 6|,to the'linkfifi and having another arm disposed substantia'lly at right {angles to the lever '51; a link "fizfpivoted as at 63* on the farelid *of'the arm and another link 64 pivote'd'at'one end bye/pin 65 to'the link 62 and 'at'the other "end *by a pin '66 to "the lever ,5! at a point intermediate of its length. Provided on the'linksymmetrically-about the pivot axis "63 is a. gear segmentfil which 'mes'hes' with a pinionfi'flpivoted on asha'ft'fifl which is axially disposed in re'lation 11118 pivot axis "58, "Secured -to this shaft, was in any suitable manner, is an indicating pointer 'lq.

In the' 'couplir'ig'mehanism -justdescribed the arrm 60' of the lever "50, the lir'rks 62 -'-a nd 84, and the "lever '51 'constitutes a" link 'structure jointed substantially in parallelogram form. Thisstructure, like thatpf the coupling mechanism {M heretofore I described, has the characteristic that a change in the angle between twoadjacent links of the structure is accompanied by a like change in each of the other angles of the structure; and moreover that such angular change is represented also by the extent ;of the turning of the gear segment 6'! about itspivot axis 63 on the arm 60. Thus angular movements between the lever 51 and arm 60', suchas may be caused by a difference in the actuationsofg the Bourdon springs, will be transmitteddirectlyin. terms of angular movement of the gear segment Bl about the axis 63 and this in turn to;the pinion:68, in the ratio of the magnitude of the radius, of the gear segment to that of the pinion, and then to the indicating-pointerflm g I 1,

The magnitudes of the movement-transmitting ratios between the levers 51 and 6 th'e levers respectively connected to the Bourdon springs 18 and 49-and the indicating pointer will again differ by one dueto the planetary movement of the gearsegment-Bi about';the pivot axisiiia caused by the turning of the lever 60 about this axis. To compensate for this; inequality in the movement-transmitting ratios," in; the instant case, 1' cause the effective movement-transmitting ratios of the couplings between the Bourdon springs 48 and 49 and respective levers 51 and 60 to be inversely proportional to the'transmitting ratios of the couplings between the respective levers and the pointer. This is done by adjusting the effective length of thelevers 51 and 60, the lever being made the shorter because the coupling between this lever and the indicating pointer is the one having the lower movement-transmitting ratio. In order that the effective length of the levers 5i and 68 may be readily adjusted they are made of semi-rigid material, say for example of brass, and provided near their ends with short laterally extending portions 51a and, Wa that are turned back to terminate into short laterally extending arms 5lb. and.60b, these latter arms being pivotally connected at their outer ends, as at 59 and GI aforementioned, to the links 54 and 55 respectively. 1 It will be seen that this arrangement permitsthe arms 51b and 60b to be bent inwardly and outwardly to vary the distance between the pivot axis 58 and the pivots 59 and M respectively.

The pressure gauge 41, like the distancetype thermometer above described, may be pro--' vided with a means to prevent the gear segment 67 from being moved out of engagement with the pinion 68, and to limit the travel of the pointer it; such means may comprise a stop pin 13 on the arm 66 which is extended through an opening M in the gear segment 61 to limt the angular movement of the gear segment about the pivot Although I have herein illustrated and described my invention in terms of certain specific embodiments it will be understood that these embodiments are merely illustrative and not limitativ-e of my invention, the scope of which I now undertake to express accordingto the following claims.

I claim:

1. In an instrument of the character described comprising indicating means. actuated to move in accordance with variations in a predetermined condition and a motor element having a portion moved in response to variations in said'condition: means operatively connecting said motor element with said indicating ;means comprising four rigid links jointed together to iform a quadrilateral structure; a, fixed pivot for said structure disposed at one of the joints thereof; means operatively connecting the movable portion of said ,motor element with one of the two links jointed at said fixed pivot; gear means secured to one of the other two links of said structure; and a pinion pivoted at said fixed pivot and driven by said gear means to operate said indicating means. v j

2. In an instrument of ,the character described comprising indicating means actuated to move in accordance with variations in a predetermined condition: the combination of a motor element having a portion adapted to turn about a predetermined axis in responseto variations in said condition; a link structure comprising four rigid links jointed together in substantially parallelogrammatic form and having one of the joints thereof: held at said axis; means operatively connecting said portion of the motor element to one of the two links associated with said one joint whereby to cause said one linkto be turned about said axis in response to variations in said condition; gear means secured to, one of the other two links of said structure and arranged coaxially with that of the joint between said last-mentioned link-and the adjacent one of said .two first-mentioned links; and jmeans pivoted at said axis and driven by said gear meansto operate said indicating means, I i I 3. In aninstrument' of the character; described having indicating means actuated to move in accordance with the difierential between two predetermined conditions and including two'motor elements respectively actuated in response to variations in said predetermined conditions: a differential mechanism coupling said motor elements with said 'indicatingmeans, comprising two coaxiallypivoted driving members respec tively angularly moved about theirpivot axis, by said motor elements;each in the same direction in response to like variations in said conditions, a follower coupled to said indicating means, and coupling means providing independently operable movement transmissions between said follower and said driving members respectively, said movement transmissions having predetermined movement-effecting ratios opposite in signpand constant. in magnitude throughout the range of movement of the driving members.

4. A mechanismior difierentially couplingtwo separately actuated motor elements with an indicating means, comprising four rigid links jointed together toform a substantially parallelogrammatic structure, said structure being pivoted at an axis coinciding with that of one of; the joints thereof; means for operatively connecting the motor elements'respectively with the two links of said structure jointed at said axis; gear means secured to one .of the other two links of said structure and arranged coaxially with that of the joint between said last-mentioned linkand the adjacent one of said first two mentioned links; and a pinion pivoted at said axis and driven by said gear means for operating the indicating means. I

5. In an instrument of the character described having a movable indicating member actuated to .move in accordance with the difierential between two predetermined conditions: the combination .of two motor elements respectively having portions turned proportionately about a predetermined axis in response to variations in said conditions; and a difierential mechanism coupling said motor elements with said indicating member, comprising four rigid links jointed together in quadrilateral fo'rin" andpositioned Wi-tlrxbh' 6f the jointsthereof at said axis means respectively coup'lingthe movable portion bf said rmot'or 'ele ments -with the twd 1 ihls jdinted at said axis-"to cause said links to be turn-d respecti'v'ely about said axisin accordance with-the aria'tions in said two conditions; "a pini'omat said =akic'oupled-= to said indicating member; and gear meansmvsam structure cdoperating with -saidpinion and op'eratively associate'd wi-th the twdlink's' jolnte'd' at said axis" to cause-said ifid'icating -member to receive a movement highl y amplified 'and substam tiall'y proportional'to the:differential-"movement between said two links 1 6. In an inSti' ilIn'eIit of the charalotef desi i bd havingan ihdicatlhg meIhber actuatewto move in accordance with the differential :betweengtwts pressures 'and substantially duplicate Bou'riio'n springseoaxiauvarranged and respectively abtl'l-l ated 'in responseto the 'variatiofls' in-said pres:

sures: adifierentil mechan'ism for coupling said Bour'don springswitlfi sai'd in'dfcatiiig meahs; comprising four-"rigid -link's jointed to emer in quadrilateral fomi and Having o'n'ofthe joints thereof positioned lat-the axis bfsa'id' Bburdbn sppmgs;

the angle 3 between said' driving controlled in accofdaiic mutanwareaencwna the actuations' 3 etween -"said--- 5 two seamen indicating member "and -pivbtd ajt th Xi-s'of ivotlifg' of said'drivin memkirs', an gearineans' coupH-m; said driving membefs witn said *biniofi-and--' cans ing the pinion-"to redeiile sin-angular amplified movement substantially pro'portional- -to' th'e' difi- 5 ference angularmovmen't' -between -said driving members; the parts of said ifis'trli-ineht? being arranged with-' th'e axes of pivotin'g' of "saia iridi cating member; r dial and "driving members all substantially l coinciding" withthe 1 axis" 4 of 's'aid Bourd'on springs wherebyt6 effect -'a highly corripact structural arrangementot the; instrument.

8. Inan-instrume'rit-bf 'the'eha r ter des'crihe d having an indicating pointer angu1er1& '-movab1e I relative to a dial, a Bourdon spring responsive to the temperature at a distant poiiit ahd tothe ambient temI$erature betwen the i'nst'r' and said point, and a s'eco'rid Bou'rdof1 s'p' axially arranged I to the' first and respor'i-sive to the ambient: temperature between the instru me'nt and said: pointme'a'ns 'for coul'iliiig said Bourdon springs with said -1o'ointrto causethe latter to receive"*anain1ilifiedrrrovement pldpor tional to; variations: in the" temperature at sai'd dlstant point; comprising aipair 'of substantially 7'5 t the (511971111titer described the temperature-at a pbint remote f ron'i 'the -1'n struhrefit and -includin s'eparately -actuatable motor elements: the o-- natien ora-airfares: tial 'rnebhali fisi'fi lilvlhg 6l1'6WeI- coupled to Said inidiatifi" means and two relatively movabl driving manners a'ch oupled to said followefi; the moveme trah's'rrii ttin'g ratio's of the-couplings btwen 's id fdllo w'e'r a'nd respective driving :membersfibeifig opp'osite in 'sig'n andunequal in m-ag-mtuu pineans e erativly connecting said motor elementsand driving" members--respeo tively i and llquid exparisiblmeansiaractuatingr s'aliddfiotbf elements compi i'sin'g a bulb- 10- cat'ed--='a5t saw-point; aptube cennectin said bulb with one of vsaiw moron-elements, anda second tube parallling saitl fi-i t ttllii'and 'sztledat one end-* and corinected at it's 'dppbsite endto the iothe'n of said'motor elenienti and: the volumetric capacities of 's'a-id' tubes: differifig 'by aE-predeteF nuned amounv tmcause one o aid -motor ele' ments to aetuated t'o g reaterxtent' than the other in response"- to" te'nu'aera'tu're change be .tweeni 'the ifistrmnent 'arid -said poin' whereby to compensatefor thedifierenc'i'ri t efie't oi suah='- temperarture "'change on the indicating means daused by the inequvlityof the moveme'ht-tran'smitti'fig raties of 'said Coupling-S 10C I'nan instrument of "th charac'ter'" de scribed having 'irfdicating means controlled to register the tem'ireratureat" a poiht remote from the instrumentfla'nd' including separately actu a'ta'bIeiBoIJAd''IT springsy th combination of a d-ifierential m'eoharfism mating a' folldwer coupled to saidundicatin'g' means and'twdre1ativ1y mow able 'driviri'gmeinbe'rs eaclq coupledte & said-dol lower, the movement-transmitting ratios of the coup'lln's between said follower 'andrespective driving memb'er-s 'be g OppbSit'e' in I sigri and un equaMn magn-itdd hrrea'n s "operativelyconnect ing saw "Bourdon spfingsqand 'drivih'g members respectively? 'and'-= 1iquid -expansihle -mean=s* for actuating said Bo'urdo'rp sprin'gs comprising a, bulb 'lo'eate'd "at'said- 'fioin'tg a tube'- connecting= said bulk "with" one 0f said Bourdo'n' sprih'gli and --a', second 'tubewparallelin'gsaid first tube ahd seal'ed at one end and connected at its opposite end- 176 the other of"said Bourdohsprings, and the sectional areas bf thebores 'o'f said 'tub' ingibyia prdeter'rrfified amount to *caus n' of said Bou'rdon sifir ihlsfit'o" be"'actuated to" greater extent-than trimmer in response m a temfifd tur'e chan'ge' between the instrUmefi'fi'and saia point, whereby to compensate for thefllifieiiid in the effect of such temperature change o'ri the indicating-means caus'ed by the in'equa'lity of the movement-transmitting ratios-'=- of sai'd' -cou= plings; 1 :1 II

1 1; In'an'instrumentof thbharact'er de scribe'd having FT indicti-ng- -meafis --'="af1d two separately actuated motor elements each" having portions angwa r'ly mwabre 'abofit pre etermined: a'Xls the combination of al paiir of dri' "fig members ivetedee afip' 'ofnti' ifi the regmw hfsa'id axisaria respectively operatively connected with said portions to turn proportionately with said respective portions throughout the rangeof actuation of the motor elements; and means for differentially transmitting angularmovement from said drivof said drive membersto cause the gear to turn on its pivot axis in accordance with the differing members to said indicating means comprising gear means pivoted on one of saiddriving members and .operatively connected with both said driving members to be actuated according to the difference between the angular movements of the driving members, and means pivoted at the point ence in the actuations of said motor elements; and means coupling said gear to, said rotatable member.

" -17'. In an instrument of the character described having indicating means actuated to movein accordance with the diiierential between two predetermined conditions and including two to variations. in said predetermined conditions:

of pivoting of" said driving members-and operatively connecting said gear means dicating means.

12. In a device of the character described in-; cluding an indicator: the combination of a pair of coaxially pivoted drive members, a pair of motor elements connected with said drive members respectively for angularly moving the same in relation to each other, gearing coupled to said with said inmotor elements respectively actuated in response a differential mechanism coupling said motor elements to said indicating means, comprising two coaxially pivoted driving members respectively angularly moved about their pivot axis by said motor elements in correspondence with the variations in said conditions, a follower coupledto indicator; and a parallel motion linkage including said drive members for coupling saidmotor elements tosaid gearing.

13. In a device of the character described cluding an indicating pointer and a pair of differently actuated motor elements: the combination of gearing coupled with said pointer; a parallel motion linkage coupled with said gearing; and connections between said motor elements and adjacent links of said linkage.

14. In a device of the character described including an indicator: the combination of a pair of coaxially pivoted drive members; a pair of motor elements respectively connected with said drive members to turn the members in the same direction upon similar actuations' of the motor elements; a pinion journalled coaxially with said drive members and coupled with said indicator;

a planetary gear pivoted to one of said drive members and in mesh with said pinion; and means operatively connecting the other of said drive members with said planetary gear and cooperating with the latter to produce a differential coupling between said motor elements and said indicator. 15. In a device of the character described including an indicator, and a pinion coupled to said indicator and a pair of separately actuated motor members: the combination of a pair of I drive members pivoted at the axis of said pinion and driven respectively by said motor members;

a planetary gear pivoted to one of said drive members and in mesh with said pinion; and means operatively connecting the other of said drive members with said planetary gear for imparting to said indicator a resultant movement corresponding substantially to the difference in actuation of said motor members.

16. In a device of the character described including an indicator and a pair of motor elesaid indicating means, and a linkage providing independently operable movement transmissions between said follower and said respective driving members having movement-transmitting ratios constant in magnitude throughout the operative range of movement of the driving members, said linkage being adapted to impart to said follower a net motion equal to the difference between the product of the transmitting ratio of one of said movement transmissions and the distance of movement of the respectively associated driving member and the product of the transmitting ratio of the other of said movement transmissions and the'distance of movement of the other of said driving members.

18. In an instrument of the character dei, scribed having indicating means actuated to move in accordance with the difierential between driving members respectively,-said movement,

transmissions having amplified transmittingrw tios opposite in sign and adapted to impart to the shaft an amplified movement substantially proportional to the differential movement be tween said driving members.

19. In an instrument of thegcharacter de scribed including indicating means and two sep- I arately'actuatable motor devices: the combination of separate coaxilly pivoted drive members coupled respectively to said motor devices and turned in proportion to the respective actuations of said devices in the same directions in response ments: the combination of a rotatable member coupled with said indicator; a pair of drive members each pivoted at the axis of said rotatable member and respectively connected with said motor elements; a planetary gear pivoted to one of said drive members and coupled with the other to like actuations of the devices; and oppositely act ng movement transmissions coupling said drive members to said indicating means for operating the indicating means substantially in accordance with the difierence, between the actuationsof said'motor devices.

EMIL 'r. JOHNSON. 

